The two most important factors in grilling a delicious burger are: (1) buying the right meat; and (2) cooking it correctly. Only once you've covered those two bases should other things come into consideration.
80/20 ground beef from Costco is the best value I've found (in general, Costco offers high quality meat for a very reasonable price). Some advocate 90/10 beef, which is healthier, but definitely offers less flavor; they usually make up for this with other ingredients, which is fine, but the easiest way to produce a juicy flavorful burger is to start with 80/20.
As for cooking it properly, it's a simple process of searing over high direct heat and then moving the burgers to a "cold" part of the grill and letting them cook to readiness indirectly. This is easily achieved on most gas grills with a large-enough cooking surface/ number of burners to maintain temperature without all the burners on; but on small or charcoal grills, indirect cooking may not be an option.
The last key to properly cooking a burger is a good meat thermometer. I use a
Thermapen; expensive, but well worth it. The consistent quality of all my grilled meat has increased ten fold since I bought it.
I like to taste the beef itself, so I don't do a lot of seasoning; salt, pepper, maybe a little garlic powder, but that's about it. 80/20 beef with a good sear pulled off the grill at 135 F is all I need. Now, if you have a sh!tty grill, or don't have a meat thermometer/ can't prevent over-cooking the meat, then a fancier recipe may work better. Some of the suggestions above are great for imbuing taste to an otherwise overcooked piece of meat.
